1. Field of the Invention
The present invention relates to a cooling fan used for consumer electronics or professional-use electrics or the like and improving cooling capacity and reducing size and weight.
2. Description of the Related Art
It has been conventionally required for a cooling fan used for consumer electronics or professional-use electronics or the like to improve cooling capacity and reduce size and weight. Taking a cooling fan for an automobile as an example, it is required to improve the cooling capacity by making an engine displacement large and to reduce the size and the weight from the viewpoint of scaling down a mounting space and getting a fuel consumption better. In case of improving the cooling capacity of the cooling for the automobile, an engine is disposed at the back of the cooling fan so as to disturb an airflow. Therefore, it is necessary to get an air in a diagonal flow direction in order to effectively circulate the air. However, it is required to increase a mounting angle of a blade or a vane in relation to a boss in order to obtain such a diagonal flow direction effect in a conventional axial fan. As a result, there is a problem that a rotational torque gets larger so as to lower a fan efficiency.
In an invention disclosed in a first Japanese Laid Open Patent Publication No. 3-89000, a blade has a skew angle that is set back to a leading end of the blade in relation to a fan rotating direction so as to get the air flow in the diagonal flow direction without enlarging the mounting angle of the blade, thereby improving the cooling capacity.
However, as a feature of an airflow in the automobile cooling fan, it is impossible that an air flow goes completely in an axial direction toward an engine block in a non-drive state or when there in no head wind. Rather, the airflow becomes the diagonal flow. Thus, expected effects are not obtained as is obvious from the first Patent Publication that fails to describe specific effects. That is, if there is a low pressure loss at the front of the cooling fan as in old-time cars, it is supposed that the flow toward the engine block is strong so as to enable the diagonal flow fan to have effects, as described in the first Patent Publication. However, there is a high pressure loss thereat in modern cars, so that the flow is hard to become the axial flow due to a pressure around the cooling fan or a centrifugal component by rotation of the cooling fan. Consequently, the above disadvantage occurs. Moreover, if the flow becomes the diagonal flow in the high pressure loss state, a flow toward a shroud that surrounds the cooling fan becomes strong. It may be a cause of a noise generation.
The flow toward the engine block becomes strong in a driving state as the head wind becomes large. Still, since an air volume is large due to the head wind, there is a question about necessity of increasing the air volume by getting the flow diagonal.